The two trends in the wireless communication networks, in response to the needs in supporting multiple antennas, are the wireless data transmission system that supports multiple antennas and the system that supports multiple user and multiple antennas. The latter is referred to as “multiuser, multi-input multi-output system, the MU-MIMO system. In such a system, a plurality of user devices equipped with wireless router with multiple antennas simultaneously.
In the traditional wireless communication networks, at each time slot only one user device is allowed to transmit signals to the wireless router. At this time slot, the allowable transmission rate depends on the characteristics of the communication channel between the user device and the wireless transceiver. Since the channel characteristics won't change substantially during such time slot, the transmission rate may be set at the best ever transmission rate in history. That is, the transmitting terminal selects the best ever transmission rate to transmit signals. After the transmission rate is determined, data to be transmitted are encoded in accordance with the determined rate and the corresponding header is added. Then receiving terminal then uses the information provided in the header to decode the received signals, so to obtain the transmitted data.
In order to support the MIMO system, the nowadays systems use a modified decoder design at the receiving terminal. One of the technologies used to support the MIMO system is the “zero-forcing successive interference cancellation” (ZF-SIC) technology. The ZF-SIC technology enables the router to recover the respective data received from two user devices at the same time, so that multiple user devices may transmit data in one wireless system at one time.
In using the ZF-SIC technology, however, the existing systems did not consider the impact that the MIMO system brought to the data transmission rate. In other words, in determining the transmission rate, the existing systems simply select the best known rate recorded in the related user device and transmit data using the selected rate. Such policy does not guaranty the best transmission rate, because, as having been discussed in many publications, the possible best rate of the user device does not only relate to its own channel characteristics but also to the channel characteristics of other user devices that transmit data at the same time. In addition, under the MU-MIMO environment user devices that transmit data simultaneously are not a fixed group. Any device is allowed to join or leave the group at any time. Therefore, a packet of data transmitted by a use device may be received along with the packet transmitted by any of the other user devices. It is then important for the user devices to select the right transmission rate, rather than the best transmission rate, because, if all the user devices select the best rates, the transmission rates would be too high for the receiving side to recover the packets received. In addition, under the design of the MU-MIMO system, the wrong rate used by one user device does not only influence its own packets but also impact the correct decoding of the packets of other user devices. As a result, selecting the best transmission rates does not result in transmitting data at higher speeds. Rather, the whole network could shut down, due to failure in decoding the packets of data being transmitted.